1. Field of the Invention
The present invention relates to an image encoder and a subcarrier signal generator, and especially relates to an image encoder sharing a signal source with an image signal processor, and a subcarrier signal generator generating subcarrier signals by itself.
2. Description of the Related Art
In a common color TV system, image data is in the form of image signals R, B, and G. A camera provides these image signals R, B, and G from light of different colors. FIG. 1 depicts a relation between an image encoder 1 and an image signal processor 2 of the prior art. Now refer to FIG. 1, the image signal processor 2 encodes these image signals in a predetermined ratio to output a Y-signal, a U-signal and a V-signal. The U-signal and the V-signal are encoded in the form of a color signal C, which represents chrominance, by the image encoder 1. The Y-signal represents a brightness of black-and-white image data.
In a camera system, phase alternation line (PAL) and national television standards committee (NTSC) are most common color TV systems, wherein pulse signal sources used in NTSC system and PAL system are of 28.6363 MHz and 28.375 MHZ, respectively. As shown in FIG. 1, two pulse signal sources are used as a system clock signal CLK1 and a subcarrier signal CLK2, respectively. A phase-lock loop (PLL) 3 synchronizes the system clock signal CLK1 and the subcarrier signal CLK2 by introducing a fixed phase-difference. However, this prior art is costly and complicated.